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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Shortwave transceiver UW3DI. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications The block diagram of the transceiver is shown in fig. one. At the input of the receiver there is an attenuator with resistors R1-R3, which improves performance in the presence of interference from closely spaced stations. It is especially advisable to use it on the 7 and 3,5 MHz bands, the level of interference on which is extremely high. When receiving weak signals and no interference, the attenuator can be turned off by the Vk1 switch. The connection of the input circuit with the antenna is autotransformer. When switching from range to range, the connection with the antenna does not change, which makes it possible to simplify switching without a noticeable loss of sensitivity. The input circuit is tuned by capacitor C117.
In the anode circuit of the high-frequency amplifier lamp (L1), a switchable band-pass filter L4-L13 is installed, the bandwidth of which in each range is equal to the range width. On the subbands 28 and 28,5 MHz, the same pair of circuits is used. The filter bandwidth is 1 MHz. Capacitive divider C18, C19 In the anode of the lamp L1 serves to reduce the transfer coefficient of the cascade to 2-3. The first mixer of the receiver is made on the left according to the scheme of the L2 lamp triode. At its output, a tunable three-circuit band-pass filter "of lumped selection with capacitive coupling is connected, which is weakly connected to the anode of the first and the grid of the second (L11) mixers. The transfer coefficient from the L2 grid to the L11 grid is about 1,5-2. A deliberate reduction in the transmission coefficient of the RF amplifier and the first mixer to the minimum possible values from the point of view of maintaining high sensitivity leads to an improvement in the real selectivity of the receiver when exposed to crosstalk. This is also facilitated by the lack of gain controls in the first two stages. The range quartz oscillator is assembled on the right half of the L2 lamp. The generator operates at the fundamental frequency and odd harmonics of the quartz resonator. In practice, when using conventional quartz plates, it generates steadily at the third harmonic. In the case of using quartz specially designed for operation on mechanical harmonics, it is possible to isolate the fifth harmonic. The generator is connected to the first mixer inductively using coils L15 and L16. The circuit formed by the L15 coil and the capacitors C20, C114 is tuned to a frequency of 15 MHz, corresponding to the 21 MHz band. When switching ranges, inductors (on the 15 and 28 MHz bands) or capacitors (on the 28,5 and 14,7 MHz bands) are connected in parallel with the L3,5 coil. The frequency of the crystal oscillator at high frequency ranges is lower than the frequency of the received signal, at low frequencies it is higher. Therefore, the sideband of the first IF signal is the opposite of the sideband of the received signal on the 7 and 3,5 MHz bands and is the same on the 28, 28,5, 21, and 14 MHz bands. The first IF of the receiver changes from 6 to 6,5 MHz simultaneously with the change in the frequency of the smooth range generator. The smooth range generator is assembled on an L3 lamp according to a capacitive feedback circuit. It operates in the range of 5,5-6,0 MHz. An L18C22 circuit is included in the anode circuit of the generator, tuned to a frequency of 5,75 MHz. The circuit is shunted by resistor R14, and its bandwidth is wide enough to ensure uniform voltage transmission in the operating frequency range. The voltage to the second mixer of the receiver is removed from the coil L17, inductively coupled with the coil L18, and fed through the capacitors C86 and C87, to the cathode of the left half of the lamp L11. The grid of the same lamp receives voltage from the concentrated selection filter. In the anode of the lamp, a frequency equal to the difference between the frequencies of the first IF and the smooth range generator is allocated. The difference frequency signal passes through the EMF and is amplified by a two-stage IF amplifier. The IF gain is regulated by resistor R26, the resistance of which determines the bias on the control grid of the lamp L4. To increase the selectivity when receiving telegraph signals, a single-crystal quartz filter at a frequency of 501 kHz with a bandwidth of about 500 Hz is included in the anode of the second stage of the IF amplifier. When receiving SSB signals, the crystal filter is turned off by contacts P1.1 of relay P1. The linear detector is assembled on the left L6 triode. A reference crystal oscillator at a frequency of 500 kHz is assembled on the right triode of this lamp. The exact frequency of the generator is determined by the frequency of the lower cutoff of the applied EMF and is set during tuning. The receiver's low-frequency amplifier is single-stage, assembled on an L lamp. The amplification to low frequencies is not adjustable. The transceiver provides the ability to independently change the receiver frequency by +10 kHz with the transmitter frequency unchanged. This is done using a capacitor * of variable capacitance C25, which is connected in the reception mode by contacts P2.1 of relay P2 instead of capacitor C26, to the smooth range generator circuit. If desired, the relay can be turned off by switch Vk2, and the reception frequency will exactly correspond to the transmission frequency. In the transmission mode, the signal from the microphone is amplified by a single-stage low-frequency amplifier (left half of the L13 lamp) and through the cathode follower (right half of the same lamp) and switch contacts P2 is fed to a ring balanced modulator made on D3-D6 diodes. The same balanced modulator receives a signal from a reference crystal oscillator. The signal received after the balanced modulator is amplified by an amplifier on an L12 lamp and fed to the EMF, after which the formed signal of the upper side band is extracted. Next, the signal is fed to the first transmitter converter, assembled on the right half of the L11 lamp. A signal is isolated in the anode, which is the sum of the frequencies of the signal formed at 500 kHz SSB and the signal of the smooth range generator. The difference frequency signal is suppressed by a lumped selection filter. After the SSB filter, a signal with a frequency of 6,0-6,5 MHz enters the grid of the L10 lamp - the second transmitter converter. The cathode of this lamp is supplied with voltage from a range quartz oscillator. In the anode circuit of the L10 lamp, a signal of the operating frequency is allocated. It passes through a bandpass filter and is amplified by an L9 lamp. Single circuits are included in the anode of the lamp, consisting of coils L24-L28 and capacitors C66-C69. The circuits are shunted by resistor R57 and have a fairly wide bandwidth. Therefore, they are tuned to the middle frequencies of the amateur bands and do not require tuning when changing frequencies. The output stage of the transmitter is assembled on an L8 lamp. To increase the stability of its operation, neutralization was applied using a capacitive divider C70, C72. A P-circuit is included in the anode of the lamp of the output stage. The capacitances of the capacitors C53-C57 are selected in coordination with the antenna. In the case of operation without an additional amplifier, you can use relay P4 for switching the antenna (shown in dotted line in the diagram), which connects the receiver input to the antenna during reception and closes it during transmission. Since this relay switches a low-current circuit, it can be low-power. When using the transceiver transmitter as an exciter, relay P4 should be excluded, and the contact of relay P3, connected to terminal K3, should be used to switch the antenna relay of a powerful amplifier. The telegraph mode of operation is carried out as follows. Using switch P2, the microphone amplifier is disconnected from the balanced modulator, and a constant voltage is applied to the latter through resistor R84. In this case, the balanced modulator is unbalanced, and a signal with a frequency of 500 kHz of the reference oscillator appears at its output. This signal is amplified by the amplifier on the L12 lamp and fed to the EMF, from the output of which it enters the first mixer of the transmitter on the L11 lamp. Telegraphic manipulation is carried out in the mixer grid circuit (socket G3). The shape of the telegraph signal is determined by the resistance of resistors R70, R71 and the capacitance of capacitor C92 / The power level both in SSB mode and in telegraph operation is controlled by changing the amplification of the L12 lamp using resistor R72. Switching Reception - Transmission is carried out using relay P3, included in the anode circuit of the right half of the lamp L14. In the Reception position, the relay is de-energized, and the circuits of the cathodes of the transmitter lamps are open. For more reliable locking of the lamps in the cathode circuit of the L12 lamp. a constant positive voltage is applied through resistors R77, R79 and R5. Resistor R6a serves to limit the magnitude of this voltage. When terminal K4 is closed (using a pedal) or when switch P2 is switched to the Transmission position, lamp L14 opens, relay P3 is activated, and the cathodes of the receiver lamps are disconnected from the common wire, and the cathodes of the transmitter lamps are closed. The transceiver provides the ability to automatically control the transmitter - the VOX system. The signal from the microphone is amplified by the low-frequency amplifier on the L13 and L14 lamps (left half), is detected by the D8 and D9 diodes and is fed in positive polarity to the grid of the right half of the L14 lamp, which leads to the opening of the lamp and the operation of the relay P3. The so-called Anti-VOX system avoids switching to transmission due to local noise or acoustic coupling of the microphone and telephone and ensures that the receiver works on the loudspeaker when the VOX system is on. Anti-VOX works as follows. The signal from the output of the receiver is detected by diodes D23 and D2 and is fed through the resistor R96 in negative polarity to the grid of the L14 lamp, thereby lowering the sensitivity of the VOX system. The power supply of the transceiver uses a power transformer with an overall power of 200-250 W. The rectifier on diodes D15-D22 provides the supply voltage to the anode circuit of the L8 lamp. It gives a voltage of the order of +700 V at a current of 150 mA. The rectifier on diodes D11-D14 provides a voltage of +270 V (on capacitor C109) at a current of 100 ma. The rectifier on the D10 diode gives a voltage of 70 V with a current consumption of 50 mA.
Design. The transceiver is assembled on a U-shaped chassis with dimensions of 300x410 mm, made of 2 mm thick aluminum. The front panel with dimensions of 180x420 mm is made of 4 mm thick duralumin and is attached to the chassis with the help of scarves. The following controls are displayed on the front panel: setting - a block of variable capacitors C29, C83, C84, C85; range switch - P1, type of work switch - P2; attenuator switch - Vk1, input adjustment - capacitor C117, receiver detuning - capacitor C25, detuning switch - Vk2; setting the output stage - capacitor C58; receiver gain - resistor R26, transmission level - resistor R73. In addition, a microphone jack is located on the front panel. The transceiver uses a quad bank of variable capacitors with a maximum capacitance of 35 pF. Such capacitors are used in radio stations R-105, R-108, etc. Capacitors C117, and C25 of the KPV type with elongated axes. Some of the plates have been removed from the capacitor C25 to obtain the desired value of the maximum receiver detuning. Neutralizing capacitor C70- for a voltage of 1000 V. Choke Dr1 - from the RSB-5 radio station, can be made independently on a frame with a diameter of 18-20 mm; contains 150 turns of PEV-2 wire 0,25 mm, winding length 90 mm. Chokes Dr2 and Dr3 contain 5 turns of wire PEV-2 0,91 each. mm and wound on MLT-2 resistors. Inductors Dr4 and Dr5 - type D-0,1 with an inductance of 80 μH. Instead of them, any others can be used, it should only be taken into account that the resistance of the inductor Dr4 should not exceed 10 ohms. Inductor Dr6- inductance of 0,5-1,0 mg must be of sufficient quality so as not to cause instability of the master oscillator. Choke Dp7 - inductance 2-5 mg. Inductor Dr8 - inductance 5 gn for a current of 100 ma. A filter choke from most TVs can be used. Relay P1, P2, P4 - type RES15, passport RS4.591.001, relay P3 - type RES22, passport RF4.500,125 or RF4.500.130. Zener diode D1 provides a stabilization voltage of about 130 V. Instead, zener diodes for a lower voltage, connected in series, or a gas-discharge stabilizer can be used, providing a stabilization voltage of the order of 120-150 V. Transformer Tr2 - type TOL-72. An output transformer from most broadcast receivers can be used. Its secondary winding is rewound so that the number of turns in it is approximately 0,2 of the number of turns in the primary winding. The data of the power transformer Tp1 are given in Table. 1. The transformer is wound on the core ШЛ25Х50. In its absence, a conventional W-shaped core can be used, but the number of turns of all windings must be increased by 30%. Table 1
As already mentioned, quartz resonators Kv1-Kv6 can be used either at the fundamental frequency or at the third harmonic. Their frequencies are listed in Table. 2 (in parentheses are the frequencies of quartz used on the third harmonic). Capacitors C123-C125, included in the circuit of the quartz oscillator, consist of a tuning capacitor of the KPKM type with a capacity of 6-25 pF and a capacitor of the KT, KM or KSO type connected in parallel to it. Table 2
Quartz Kv7 has a frequency of 501 kHz. Quartz Kv8 - 500 kHz. More precisely, its frequency is adjusted during tuning. The data of all contour coils are given in table. 3. Setting up the transceiver does not present a serious difficulty and is quite accessible to a radio amateur of average qualification who is familiar with the general principles of setting up receiving and transmitting equipment. It is necessary to note only some characteristic features. The balanced modulator provides a very high degree of carrier frequency suppression, but is very critical to the capacitance of the C88 capacitor. With a properly selected capacitance and maximum amplification of the L12 lamp, the value of the unbalanced carrier balance on the anode L12 does not exceed 0,2-0,3 V, while in case of imbalance (switch position P2 Setting}, the carrier level exceeds 30 V. The selected carrier recovery scheme for telegraph operation requires a very precise setting of the reference quartz at the cutoff of the EMF frequency response. Quite often, radio amateurs, seeking to increase carrier suppression in transmitters, set the frequency of the reference oscillator unnecessarily far from the cutoff of the frequency response, which leads to a deterioration in signal quality. In this design, such a frequency setting will also lead to insufficient buildup when working with a telegraph, since the restored carrier will be suppressed by the EMF. The correctness of the frequency setting of the reference oscillator can be checked as follows. In the Setting mode, the gain of the cascade on the L12 lamp is set so that the alternating voltage at its anode is 10 V. In this case, the voltage at the filter output should be 0,2-0,3 V. To avoid errors when measuring the voltage at the filter output, the L3 lamp must be removed from the socket. It is convenient to tune the range crystal oscillator as follows. The quartzes are removed from the quartz holders and capacitors with a capacity of 100 pF are installed in their place on the ranges of 28 and 21 MHz and 300 pF on the rest. In this case, the crystal oscillator turns into a conventional LC oscillator with capacitive coupling. Switch P1 is set to a range of 21 MHz and, by changing the inductance of the coil L15 with the help of a core, the generator is tuned to a frequency of 15 MHz. On other ranges, the anode circuit of the generator is tuned to the frequencies indicated in Table. 2. The generation frequency is controlled by the receiver. After that, the quartz is installed in its place and the generator is adjusted to achieve the required oscillation amplitude (on the cathodes of the mixer lamps, it should be 1-2 V). When using a block of capacitors from the R-108 radio station, the coupling of the concentrated selection filter circuits with the frequency of the smooth range generator is obtained without the use of coupling capacitors. It is only necessary to choose the inductance of the coil L19 and the capacitance of the capacitor C27 in such a way that the frequency overlap of the generator is 520-560 kg c. Bandpass filters are tuned at the middle frequency of each band in Transmit mode. The signal from the GSS is fed to the grid of the L10 lamp. One of the filter circuits is shunted with a resistor of about 2 kΩ, and the unshunted circuit is tuned to the maximum voltage at the anode of the L9 lamp. After that, the resistor is transferred to the newly tuned circuit and the second circuit is adjusted in the same way. The neutralization of the final stage is carried out on the 28 MHz range by selecting the capacitance of the capacitor C72. Since on the ranges of 7 and 3,5 MHz the frequency of the crystal oscillator is higher than the frequency of the range, and on the ranges of 14, 21, 28 and 28,5 MHz it is lower, the scale of the ranges of 7 and 3,5 MHz is the reverse of the scale of the high-frequency ranges. This should be taken into account when working with the transceiver. Table 3
Author: Yu. Kudryavtsev; Publication: N. Bolshakov, rf.atnn.ru
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